Moving to placement group

[kung]

Scenario: “high-performance computing (HPC) application…improve the network performance between the controller instance and the EC2 instances in the placement group”

Correct answer: “Stop the custom cluster controller instance and move it to the existing placement group”

But there might not be any instance capacity available at that moment?

I believe it is advised to create all instances of a cluster placement group in one go?

“We recommend that you launch your instances in the following way:
Use a single launch request to launch the number of instances that you need in the placement group.
Use the same instance type for all instances in the placement group
If you try to add more instances to the placement group later, or if you try to launch more than one instance type in the placement group, you increase your chances of getting an insufficient capacity error.”

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/placement-groups.html

So wouldn’t that hint to the answer

“Terminate the custom cluster controller EC2 instance and stop all of the running instances in the existing placement group. Move the cluster controller instance to the existing placement group and restart all of the instances.”

as the preferred option to choose?

Cheers,
Robert

[TutorialsDojo-Support]

Hi Robert,

Thanks for the feedback.

You are correct that if you want to add an instance to a placement group, it is recommended to use a single launch request to launch the number of instances you need.

However, this is a custom controller EC2 which may not be the OS setup (or installed applications) as the instances inside the Placement-group. You will want to lessen your work and don’t want to recreate that custom controller. So you can first try to add it manually to the existing placement group. AWS allows you to move an EC2 to an existing placement group (see link below).

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/placement-groups.html#change-instance-placement-group

The chance of getting an insufficient capacity error is not fixed. If it is just one instance, there is a good chance that the current placement group host can accommodate another instance.

Hope this helps.

Regards,

Kenneth Samonte @ Tutorials Dojo